1. Field of the Invention
The present invention relates to a monitoring technology for monitoring whether or not trouble has occurred in an apparatus connected to a network, such as a computer, a telephone exchange system or a process controller. Particularly, the present invention relates to a mutual monitoring technology in which an apparatus connected to a network monitors whether or not trouble has occurred in another apparatus connected to the network.
2. Description of the Related Art
Technologies in which an apparatus connected to a network monitors another apparatus connected to a network include the following technologies.
In the related art described in Japanese Patent Published Application No. 2001-75837, each computer to be monitored regularly sends to other computers a packet including its identifier. The packet is sent by broadcast or multicast. Each computer contains a component information storing portion where identifiers of all computers to be monitored are registered. If the identifier of a computer is registered in that storing portion of other computers and a packet from that computer has not been received within a predetermined time, the other computers determine that trouble has occurred in that computer from which a packet has not been received.
This related art has a problem of increasing the load on a network because it is necessary to send a packet by broadcast or multicast. Further, this related art has a problem of requiring a large memory size for the component information storing portion if there are a large number of computers to be monitored. It is also not easy to add a new computer to be monitored. This is because it is required that the identifier of all computers to be monitored should be registered in the storing portion of each computer for use in broadcast or multicast.
In the related art described in Japanese Patent Published Application No. 2002-312199, each computer to be monitored has a list showing an order of inquiry of each computer. Namely, in this list, identifiers of all computers to be monitored are linked by pointers in an order of inquiry. In this list, the pointer of the last computer shows the identifier of the first computer. That is, this list is a ring type order list. Each computer sends back a response upon inquiry from another computer. Each computer recognizes the first computer to which the inquiry is made based on that ring type order list retained by itself, and inquires of that first computer. If a response is given to that inquiry from the first computer, it is determined that the first computer is normal, and processing is ended. If no response is given from the first computer, it is determined that trouble has occurred in the first computer. In this case, further, each computer inquires of the second computer in the order of inquiry based on the ring type order list. If a response is given from the second computer, it is determined that the second computer is normal, and processing is ended. In this case, the second computer which sends back a response, performs processing same as the processing described above based on the ring type order list retained by the second computer.
This related art has a problem of requiring a large memory size when there area large number of computers to be monitored. It is also not easy to add a new computer to be monitored. This is because it is necessary for each computer to retain the ring type order list in which identifier of all computers to be monitored is linked by pointers.